Method and apparatus for determining the configuration of a cellular transmission system

ABSTRACT

A method for operating a data processing system to determine the operational parameters of a communication system between an REC and an RE that utilizes a CPRI data link for communication. The data processing system is synchronized with the CPRI frames and determines a plurality of CPRI frame characteristics from the CPRI frames by examining a plurality of predetermined locations in the CPRI frames. The plurality of CPRI frame characteristics for one or more of the CPRI frames, and a first model of the communication system are used to generate a first broadcast frame that would be generated by the one or more CPRI frames if the first model accurately described the communication system. The first broadcast frame is tested to determine if the first broadcast frame is consistent with the first model. If the broadcast frame is inconsistent, a new model is chosen and the process repeated.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/781,124 filed on Feb. 28, 2013 and claims prioritytherefrom. Further, that patent application is incorporated herein byreference in its entirety.

BACKGROUND

Passive monitoring systems for communications between transmitters incellular telephone systems are used by operational support systemproviders to monitor the traffic and sometimes the content of thecommunications on such transmitters, referred to as user equipment (UE)in the following discussion.

Ideally, monitoring is performed without the active participation of thecellular provider or the UE that is being monitored so that the cellularprovider does not need to alter its operation during monitoring. Hence,the monitoring system preferably taps into the data flow between thecellular system and the UE. Monitoring systems for communications inearlier cellular systems tapped a point in the data flow that is nolonger available in 4G networks. In addition, the data that is availablein 4G networks is in the form of baseband carrier data that encodes theentire set of transmissions between the cellular transmitter and all ofthe UE in a cell in a manner that can be easily utilized by a radio headtransmitter without introducing delays into the transmissions. Tomonitor any particular transmission, the monitoring system must know themanner in which the communication link that is available for tapping isorganized. This organization can vary from cell to cell in a system, andhence, must be discovered by the monitoring system if the cooperation ofthe cellular provider is to be avoided.

Remote radio heads and remote radio head controllers use a Common PublicRadio Interface (CPRI) that typically goes through a set ofinitialization stages when first connected together to negotiate anumber of important characteristics of the communication link, such asline rate, CPRI word length, number of antenna carriers, IQ sample sizefor downlink and uplink, and type of padding. While systems that monitorthe startup phase can be used to provide the needed information on theorganization of the data flow, these systems must have a probe in placeduring the startup phase of the system. Since a passive CPRI probe maybe connected to such interfaces at any time after the system has beenconfigured, it cannot be assumed that the probe will observe thisinitial negotiation phase to determine the needed parameters. Thus aprobe that can learn these parameters from the observed byte stream isneeded.

In addition, the probe must also learn the type of communication systemthat is being implemented using the CPRI frames to encapsulate the datathat determines the broadcast frames that are broadcast by the cellantennae. CPRI encapsulation is used to implement radio communicationsthat satisfy a number of different communication models. Exemplarycommunication systems include “long term evolution systems” (LTE),communication systems, “Universal Telecommunications systems” (UMTS),and “Global Systems for Mobile Communications” (GSM). Each of thesesystems map the data that defines radio frames that are utilized by theUE in a different manner. Hence, without knowing which communicationsystem is being implemented, the probe cannot fully decode thetransmissions.

SUMMARY

The present invention includes a method for operating a data processingsystem to determine the operational parameters of a communication systemwhich includes a Radio Equipment Control (REC) and a Radio Equipment(RE) that communicate with one another over a data link utilizing CPRIframes. The RE transmits and receives broadcast frames. The method ofthe present invention includes synchronizing the data processing systemwith the CPRI frames and determining a plurality of CPRI framecharacteristics from the CPRI frames by examining a plurality ofpredetermined locations in the CPRI frames. The plurality of CPRI framecharacteristics for one or more of the CPRI frames, and a first model ofthe communication system are used to generate a first broadcast framethat would be generated by the one or more CPRI frames if the firstmodel accurately described the communication system. The first broadcastframe is tested to determine if the first broadcast frame is consistentwith the first model.

In one aspect of the invention, CPRI frames are searched for a firstbyte in a data stream on the data link that determines a hyper-frameboundary. Predetermined locations relative to the first byte areexamined to determine the number of bytes between the hyper-frameboundary and the first byte of a subsequent CPRI frame on the data link.CPRI frame characteristics that are independent of the first model arethen determined, such as the CPRI line bit rate used in transmissions onthe data link and the number of antenna carriers.

In another aspect of the invention, providing the first broadcast frameincludes extracting IQ data values that depend on the first model fromone of the CPRI frames, and determining symbols specified by theextracted IQ data values that would be transmitted by the firstbroadcast frame if the first model accurately describes thecommunication system. The determined symbols can include symbols in thefirst broadcast frame that allow a UE in a cell transmitting the firstbroadcast frame to synchronize the UE with transmissions from the cell.

In yet another aspect of the invention, testing the first broadcastframe includes determining symbols in the first broadcast frame andcomparing the determined symbols with a value encoded in a control blockin one of the CPRI frames.

If the first broadcast frame is not consistent with the first model, asecond model for the communication system that is different from thefirst model is chosen. Using the plurality of CPRI framecharacteristics, and the second model, a second broadcast frame thatwould be generated by the one or more CPRI frames if the second modelaccurately described the communication system is determined. The secondbroadcast frame is then tested to determine if the second broadcastframe is consistent with the second model.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the manner in which an IQ Monitor (IQM) according tothe present invention is inserted into the communication link between anRF module and an REC module.

FIG. 2 illustrates the division of the band in the frequency domain.

FIG. 3 illustrates the organization of an LTE data frame having a 20 MHzbandwidth.

FIG. 4 illustrates the relationship between resource blocks and resourceelements.

FIG. 5 illustrates the CPRI frame structure that is transmitted on anoptical or electrical link as a serialized data stream.

FIG. 6 illustrates the organization of the control block.

FIG. 7 illustrates a basic frame in which the additional bits arelocated at the end of each basic frame.

FIG. 8 is a flow chart of the basic method by which the presentinvention determines the structure of the CPRI frames and LTE frames byobserving the data on the CPRI link.

FIG. 9 is a flow chart of step 201.

FIG. 10 is a flow chart of step 202.

FIG. 11 illustrates the third step of the flow chart shown in FIG. 8.

DETAILED DESCRIPTION

The manner in which the present invention provides its advantages can bemore easily understood with reference to a particular communicationsystem. The manner in which the present invention can be extended toother communication systems will then be discussed in more detail. AnLTE cellular network is a type of 4G cellular network. Thecommunications between the network interface to a cell and the UE areseparated into a baseband digital processing function and the actual RFfunctions of the antenna system such as filtering, modulation of thecarrier for the cell in question, frequency conversion andamplification. These functions are separated into two modules, an RECmodule that performs the digital processing function for generating adigital stream that is transmitted to the UE after upconversion and anRE module that provides the RF functions and interfaces to the UEsthrough the cell antennae. An RE module is located in each cell. The REmodule is connected by high-speed point-to-point serial links to the RECmodule that is typically at a location that is remote from that of theRE.

The REC module and RE module exchange data in a first framed format thatincludes a temporal sequence of digital in-phase and quadrature (IQ)baseband data. In essence, the REC module generates a digital datastream consisting of the IQ baseband values that, after upconversion,are to be transmitted by the RE module. Similarly, the RE moduledownconverts the received signals from the cell to a stream of IQbaseband values. For the purpose of this discussion, IQ baseband valuesare defined as a sequence of IQ values occupying a frequency band with acenter frequency at or near DC. In addition, control data aremultiplexed onto the high-speed digital bus within the frames. Twostandards have been proposed for the communications between the RECmodules and the RE modules. These are commonly referred to as the CPRIand the Open Base Station Architecture Initiative (OBSAI).

From the point of view of the UE in the cell, the transmitted IQ valuesform a sequence of frames having a plurality of adjacent frequency bandsin which each frequency band is used to transmit or receive a sequenceof digital symbols. These frames will be referred to as “LTE” frames inthe following discussion. The data for each LTE frame is provided in acorresponding CPRI frame. In the present invention, a cell monitorfunction is implemented by inserting an IQM into the digital linkbetween the REC module and the RE module using a passive splitter. TheIQM has access to all of the baseband data, and hence, can monitor thecommunications to and from any UE being serviced by the RF transmitterin the cell without requiring downconversion of the RF signals. Inaddition, the present invention takes advantage of the known protocolsfor data exchanges between the UE and REC modules, and hence, thepresent invention can selectively demodulate and decode the baseband toaccess the data for a UE of interest without having to demodulate anddecode the entire CPRI frame.

Refer now to FIG. 1, which illustrates the manner in which IQM 57according to the present invention is inserted into the communicationlink between an RF module and an REC module. In cell 50, the function ofthe traditional transmission node between the cellular system and UE 21is provided by antenna 51, RF module 53, and base station main unit 54.RF module 53 is connected to antenna 51 via an RF link 52. RF module 53is connected to base station main unit 54 by digital link 55. RF module53 provides the functions of the RE module discussed above, and basestation main unit 54 provides the functions of the REC module discussedabove. A passive splitter 56 is introduced into digital link 55.

Passive splitter 56 will in general be of a type that depends on thenature of digital link 55. For example, if digital link 55 is an opticallink, an optical splitter is preferred. Such optical or electricalsplitting is common practice in modern networks, and hence, will not bediscussed in detail here.

As noted above, the data on digital link 55 is in the form of CPRIframes, and the transmitted data on antenna 51 is organized as LTEframes. The CPRI frames also include some control words whose functionswill be discussed in detail below. The corresponding LTE frame can beviewed as a plurality of sub-carrier frequencies. The sub-carriersinclude a set of sub-carriers that are used to send 140 symbolscorresponding to each CPRI frame. The manner in which the remainingsub-carriers are used will be discussed in more detail below. Eachsymbol is sent in a predetermined time period. Given a time period, theCPRI frame corresponding to the LTE frame, and the structure of the CPRIframes and LTE system, a set of IQ time domain values in the CPRI framecan be identified. If this set is subjected to a fast Fourier transform(FFT), the contents of each sub-carrier can be ascertained for the timeperiod in question without requiring that the IQ samples for other timeperiods be demodulated.

To monitor the LTE communications in an IQM, the IQM must be able toidentify frames on the CPRI link, know the structure of those frames,and know the structure of the LTE system that is utilizing those frames.While these structures are known to the REC and RE modules, thesestructures are not necessarily known by the IQM when the IQM is firstconnected to digital link 55 discussed above. Hence, the IQM must beable to obtain this information by observing the traffic on digital link55.

The observable signals on the link between RF module 53 and base stationmain unit 54 are digital values that are organized into CPRI frames.Each CPRI frame includes some control words and sequences of I and Qvalues that are to be transmitted by RF module 53 after beingupconverted in frequency to the correct frequency band corresponding toantenna 51. Similarly, CPRI frames from RF module 53, after beingdownconverted to baseband data, are organized as sequences of I and Qvalues that have been received from the UE within the cell. Thisbaseband data is returned to base station main unit 54 where the data isdemodulated to determine the symbols sent by the UEs in the cell duringthe time period corresponding to the CPRI frame in question.

As noted above, the data communicated in the CPRI frames defines asequence of frequency channels in which each channel sends or receivesdigital data in the form of “symbols” over the time frame of each CPRIframe. The symbols are sent serially on each channel. Each symbol issent in a time “slot” on the frequency in question. The frequencies forma broad band of frequencies, and hence, will be referred to assub-carriers in the following discussion. During any one CPRI frame,each channel sequentially receives or sends a plurality of symbols.

From a monitoring point of view, IQM is interested in a specific subsetof the symbols being sent and received by RF module 53. In general,there are a number of symbols of interest in each frame. The problem ofaccessing these symbols without decoding the entire frame can be reducedto determining a time period in the frame in which at least one of thesymbols of interest is being sent or received, determining the subset ofIQ values corresponding to that time period in the frame, and thenapplying an FFT to that subset of IQ values to determine the symbolssent in each sub-carrier at that time. In general, there will bemultiple symbols of interest at the time in question, since thesub-carriers are allocated blocks of adjacent sub-carriers as will beexplained in more detail below.

To perform this function, the IQM must “know” a number of parametersthat determine the organization of the LTE frames and the correspondingCPRI frames. The structural organization of the LTE frames and CPRIframes varies from cell to cell in a network. For example, different LTEcells utilize different numbers of sub-carriers. The correspondingnumber of IQ samples and size of the FFT depend on the number ofsub-carriers. These parameters will be discussed in more detail below.For the purpose of the present discussion, it is sufficient to note thatthese parameters must be determined by viewing the CPRI frames, whichhave an organization that does not lend itself to a simple analysis.

In addition, to monitor communications between a specific UE and thecellular system, the allocation of sub-carriers and slots in any givenframe that are directed to that UE must be determined. Thisdetermination is made by monitoring specific dedicated channels thatspecify the allocation of sub-carriers and slots in the various frames.The details of these monitoring functions are not central to the presentinvention, and hence, will not be discussed in detail here. The readeris directed to U.S. patent application Ser. No. 13/433,173 filed on Mar.28, 2012, which is hereby incorporated in its entirety by reference andwhich discusses these monitoring functions in detail.

The manner in which the present invention provides its advantages can bemore easily understood with reference to the structure of the CPRIframes and the LTE frames, since translation between the data in thesetypes of frames is essential to the operation of an IQM. Communicationsin the LTE system are sent utilizing a frequency band that is dividedinto a contiguous block of sub-carrier frequencies. Each sub-carrier isused to send or receive a sequence of symbols, each symbol occupying apredetermined time slot on the sub-carrier in question. A symbol is adigital value between 0 and N−1. The corresponding transmission on thesub-carrier in question is contained in a sequence of IQ values that aretransmitted during the time slot in question. These sequences of IQvalues are communicated on the link between the REC and RE componentsdiscussed above. Hence, to decode a symbol corresponding to a givensub-carrier and time slot, the IQM must know where the sequence of IQvalues that define that symbol is located in the CPRI frame. In general,the sequence of IQ values will determine a symbol in all of thesub-carriers. The sequence in question is converted to the symbols inthe various sub-carriers using an FFT. Accordingly, an IQM must know thenumber of sub-channels in the structure of the specific LTEconfiguration in the cell being monitored and the structure of thecorresponding data in the CPRI frames.

To decipher the setup of the LTE system, the present invention mustfirst determine the structure of the LTE system that is receiving theCPRI frames. To simplify the following discussion it will be assumedthat there are four channel models corresponding to bandwidths of 5 MHzto 20 MHz in increments of 5 MHz. The manner in which the presentinvention can be expanded to deal with other channel models will beapparent from the following discussion. Each band is divided into aplurality of sub-carriers. Some of these sub-carriers have fixedfunctions, while others are allocated on a frame-by-frame basis forcommunications with specific UE. These parameters of the various LTEsystems are summarized in Table 1, below.

TABLE 1 Channel Bandwidth 5 MHz 10 MHz 15 MHz 20 MHz No. of Sub-carriers300 600 900 1200 No. of Resource Blocks 25 50 75 100 Sampling Rate (MHz)7.68 15.36 23.04 30.72 FFT Size (payload) 512 1024 1536 2048 Datasub-carriers (+DC 300 600 900 1200 sub-carrier) Guard sub-carriers 212424 636 848 Cyclic Prefix Length Normal 40/36 80/72 120/108 160/144Extended 128 256 384 512 Samples per Slot 3840 7680 11520 15360 Totalsamples per 10 ms 76800 153600 230400 307200

For example, for a 20 MHz bandwidth model, there are 1200 sub-carriers.Data is decoded from a sequence of 2048 IQ time samples to arrive at thesymbols in 1200 sub-carriers by performing an FFT on time samples takenat the indicated sampling rate. In addition, there are a number of“guard sub-carriers” whose functions will be discussed in more detailbelow. Each slot is represented by 15360 IQ samples in a CPRI frame.These samples are divided into the samples that provide the symbolvalues and various other bits whose functions will be discussed in moredetail below. Given that the IQM needs to examine the symbols at aspecific slot, the IQM must be able to determine the location of the IQtime samples within the frame that corresponds to the slot in question,and hence, must know the details of these other bit allocations.

While the minimum data entry of interest is a symbol in a particulartime slot on a particular carrier, the minimum data capacity that isallocated to a function or user is a “resource block” (RB) whichcorresponds to a plurality of contiguous sub-carriers and a plurality ofsymbols on each of those sub-carriers. Since the details of the dataallocations are not central to the present invention, the structure ofsuch transmissions between the cellular system and the UE will not bediscussed in detail here.

To provide protection against interference from neighbouring cells in acellular system, the sub-carriers at the high and low ends of thechannel are not used for data. These sub-carriers will be referred to asguard sub-carriers in the following discussion. In addition, a number ofreference/pilot sub-carriers are reserved, and hence, are not availablefor transmitting data. The various sub-carriers are shown in FIG. 2,which illustrates the division of the band in the frequency domain. Thelower and upper guard sub-carriers are shown at 31 and 32, respectively.Exemplary reference/pilot sub-carriers are shown at 34. A DC sub-carrierthat is also used as a pilot/reference sub-carrier is shown at 35.Finally, the data sub-carriers are shown at 33. As will be discussed inmore detail below, these reference sub-carriers can be used indetermining the specific LTE configuration that is being utilized by theRE, as some of these sub-carriers have locations that are different fordifferent LTE configurations.

Refer now to FIG. 3, which illustrates the organization of an LTE dataframe having a 20 MHz bandwidth. Each frame is 10 ms long and is dividedinto ten sub-frames. Each sub-frame is, in turn, divided into two“slots”. Hence, there are 20 slots in each frame. Each slot, in turn, isused to send a plurality of symbols. The number of symbols depends onthe manner in which the symbols are augmented to protect againstinter-symbol interference.

In the time domain, a form of guard band is also utilized to reduceinter-symbol interference. A cyclic prefix (CP) is added to thebeginning of each time period as shown at 39 and 41. The CP is just arepeat of a number of samples from the end of the samples representingthe symbol. The size of the CP is different for the first symbol of aslot. In the example shown in FIG. 3, 160 samples are used in the firstslot, and 144 samples are used in each of the remaining slots. Thenumber of samples in the CP depends on both the bandwidth of the LTEsystem and the type of CP used (normal or extended). In addition, thenumber of symbols per slot depends on the type of CP in use. Forexample, in a 20 MHz LTE system that utilizes the extended prefix, onlysix symbols are sent in each slot. In contrast, if the normal CP isused, seven symbols are sent in each slot.

The time domain IQ samples that communicate the actual symbol values areshown at 42. For a 20 MHz bandwidth system, there are 2048 samples thatdefine the symbol at that particular time in each of the sub-carriers.In the instant example, there are 2048 such samples corresponding to the1200 sub-carriers and 848 guard sub-carriers. The period, Ts, is thebasic time unit of the system and all other time periods are multiplesof Ts. For LTE, Ts=1/30.72 μs.

Refer now to FIG. 4, which illustrates the relationship between RBs andresource elements. Transmissions in LTE are scheduled in units of RBswhich for normal mode CP represent 12 consecutive sub-carriers by sevensymbols in time. An RB occupies one slot. This represents a nominalbandwidth of 180 kHz for a duration of 0.5 ms or one slot as describedearlier. A resource element is the smallest defined unit which consistsof one sub-carrier during one symbol interval. It should be noted thatCPs have been excluded from the figure. Thus the 2048-point FFTgenerates 1024 sub-carriers of which 1200 are used as data carriers oneither side of the DC carrier, and the rest are used as guardsub-carriers as explained above. The minimum possible capacityallocation period for both uplink and downlink in LTE systems is 1 ms,which corresponds to two RBs within a single sub-frame. Thus resourcesare allocated over two consecutive RBs within the same sub-frame.

To monitor any particular UE communications, the IQM must know the RBsthat are utilized for those communications. It should be noted thatthose RBs change from LTE frame to frame. When a UE initiates contactwith the cellular system, the UE sends messages on predeterminedchannels that occupy particular resource elements in each frame. The UEis given an identification number which is used in the variouscommunications. The UE monitors particular channels for messagesdirected to that UE. Each channel has a predetermined set of resourceelements in each frame. When the UE is to receive data, the cellularsystem sends the identification of a future frame and RBs in that framein which that data is to be sent to the UE. The UE then decodes thoseRBs in the identified frame. Similarly, when the UE wishes to send data,it makes a request on a predetermined channel and the system sends it amessage indicating the RBs and frames on which it is to transmit. Asnoted above, for the purposes of the present discussion, it issufficient to note that the IQM can identify resource elements that areto be monitored by first monitoring specific control channels forcontrol communications of interest and then monitoring the resourceelements specified in those control communications. Each of these stepsidentifies one or more resource elements that are encoded in known CPRIframes and requires the IQM to demodulate the IQ data corresponding tothose resource elements to obtain the symbols in question.

Hence, an understanding of the CPRI frame structure is needed to extractthe information needed by the IQM in decoding the transmissions. TheCPRI frames can also have a plurality of structures that must bediscovered to determine the location of the IQ data in a CPRI frame fora symbol of interest.

Refer now to FIG. 5, which illustrates the CPRI frame structure that istransmitted on an optical or electrical link as a serialized datastream. The communications are organized into CPRI frames that are sentserially over the link. Since the link is a point-to-point link, theframes do not have headers that specify the source and destinationaddresses, since these locations are known. Hence, the data observed ona link is a logical encapsulation or packetization of I and Q sampleswith implied or “abstract” framing.

A CPRI frame is always 10 ms long and abstractly contains 150hyper-frames 101. Each abstract hyper-frame is made up of 256 basicframes 102. The hyper-frames and basic frames are referred to asabstract hyper-frames and basic frames because there are no headers ortrailers associated with these to delineate them. However, to simplifythe following discussion, the “abstract” labeled is omitted. Each basicframe 102 is subsequently made up of 16 words 103. The word length isdependent on the line rate that is discussed below. It should be notedthat the number of bytes in a CPRI frame depends on this word size,since there are always 150 hyper-frames and 256 basic frames in eachhyper-frame. When referring to a specific basic frame in a CPRI frame, anotation in the form z.x.n is used, where z is the hyper-frame number inthe CPRI, x is the basic frame number within hyper-frame z, and n is theword number within that basic frame.

The first word of each basic frame is referred to as the “control word”.This is the only form of delineation that can be observed in thepacketized IQ samples. In one aspect of the present invention, thesecontrol words are utilized to identify basic frames in the transmissionson the data link and to synchronize the IQM with the REC.

The 256 basic frames in each hyper-frame have a collection of 256control words. The number of control “bytes” in a hyper-frame depends onthe word size. These control words form a control block having 64sub-channels with four control words for each sub-channel. The termcontrol block is defined to be this collection of control words. Thesesub-channels are shown in FIG. 6, which illustrates the organization ofthe control block. It should be noted that the control words are notadjacent to one another, but rather distributed throughout thehyper-frame. The index in the hyper-frame of a control word x is givenby X=Ns+64*Xs, were Ns is the sub-channel number that runs from 0 to 63,Xs is the word number for that sub-channel that runs from 0 to 3. Theindex of selected control words is shown in FIG. 6. These controlsub-channels are used to support a number of protocols to help establishthe CPRI link and synchronize remote radio heads with basebandprocessing remote radio controllers, maintenance of the link state,vendor specific protocols and space for future extensions. The presentinvention utilizes sub-channel 0, which carries the “Comma Byte” whichis the same for all hyper-frames and other control entries tosynchronize the IQM to the REC and extract data needed to determine thestructure of the CPRI frames and the corresponding LTE frames.

The CPRI frames between an REC and RE can include multiple IQ datachannels in which each IQ stream represents the digital baseband dataassociated with the transmission and reception of a single wirelesscarrier at an antenna in the REC. To support such systems, the CPRIframes are divided into IQ data channels. Time Division Multiplexing(TDM) is used to simultaneously support multiple independent IQ streams.Each IQ stream represents the digital baseband data associated with thetransmission and reception of a single wireless carrier at an antenna.In the CPRI specifications, these IQ sample streams are referred to asantenna carriers and represent independent IQ data channels. Since thenumber of antenna carriers varies depending on the specific cellularorganization, the IQM must determine if there are multiple antennacarriers and which antenna carrier includes the data of interest. Inaddition, there may be reserved bits at the end of each CPRI basic framethat are not used for transmitting the antenna carriers.

The organization of an exemplary basic frame having multiple antennacarriers is shown in FIG. 7, which illustrates a basic frame in whichthe additional bits are located at the end of each basic frame. Hence,if there are multiple antenna carriers, the IQM must determine whichantenna carrier is being used for the antenna that is communicating withthe UE of interest. This further complicates the discovery process.

The number of bits per basic frame that can be used to transport antennacarriers is then dependent on the line rate and word size. Theseproperties are summarized in Table 2, showing line rate, word size andavailable IQ data blocks in bits. Note that the IQ data block sizescorrespond to 15 CPRI words as the first word per basic frame is thecontrol word mentioned earlier. These parameters must be discovered bythe IQM.

Antenna carriers or IQ data channels are then multiplexed into these IQdata blocks. The number of carriers per data block is dependent on thesample width used for I and Q values, the frequencies being multiplexedonto the data blocks and of course the capacity of the CPRI line rate inuse which determines its IQ data block size.

TABLE 2 Number of IQ bits per basic frame as a function of CPRI linerates Line Rate (Mbps) 614.4 1228.8 2457.6 3072 4915.2 6144 9830.4 WordSize 8 16 32 40 64 80 128 IQ Data 120 240 480 600 960 1200 1920 Block(bits)

The CPRI specification allows for the use of a number of differentmapping methods for different cellular standards as well as how theseantenna carriers are packed into the IQ data blocks and how padding ismultiplexed in between antenna carriers or at the end of the useful IQdata bits. Equally, equations exist to derive how many samples S,representing I and Q pairs per antenna carrier of a particular wirelessstandard at a particular frequency are required per basic frame. Thislatter period is referred to as the duration K in basic frames. Tosimplify the following discussion, it will be assumed that a densepacking mode is applied and, if stuffing bits are required, they appearat the end of the basic frame. Further, it is assumed that an I and Qsample width of either 16 or 15 bits for the downlink and 8 bits for theuplink are used. While LTE can support bandwidths of 1.25 MHz and 2.5MHz it is more likely that the bandwidths lie in the 5 to 20 MHz range.If the IQM fails to decode CPRI frames utilizing these assumptions,additional searches can be done as discussed in more detail below. Therelationship between S, K, LTE bandwidth, and different numbers ofcarrier channels is shown in Tables 3 and 4, for I and Q sample widthsof 16 and 15 bits in the downlink (DL) direction, respectively.

TABLE 3 Data channels and sample width per basic frame for 16-bit DL Iand Q width. LTE Number of AxC per IQ data block, per basic frameBandwidth 120 240 480 600 960 1200 (MHz) S K IQ IQ IQ IQ IQ IQ 5 2 1 1 37 9 15 18 10 4 1 — 2 3 4 7 9 15 6 1 — 1 2 3 5 6 20 8 1 — — 1 2 3 4

TABLE 4 Data channels and sample width per basic frame for 15-bit DL Iand Q width. LTE Number of AxC per IQ data block, per basic frameBandwidth 120 240 480 600 960 1200 (MHz) S K IQ IQ IQ IQ IQ IQ 5 2 1 2 48 10 16 20 10 4 1 1 2 4 5 8 10 15 6 1 — 1 2 3 5 6 20 8 1 — 1 2 2 4 5

Taking these considerations into account, Tables 3 and 4 show for thechosen LTE bandwidths the sample size S of the antenna carrier per basicframe period K. For each IQ data block size, they also show thetheoretical maximum number of antenna carriers at a given frequency thatcan be multiplexed per basic frame. For LTE it is clear that K, due tothe CPRI basic frame timing characteristics is always one, and S can bederived from the number of samples per 10 ms LTE frame for each of thefrequencies. In particular, S is the total number of samples per 10 msLTE frame as shown in Table 1 divided by the number of basic framestimes the number of hyper-frames in each 10 ms in each CPRI frame. Forexample, the sample size per antenna carrier for a 20 MHz bandwidth LTEsystem is 8 IQ values.

Refer now to FIG. 8, which is a flow chart of the basic method by whichthe present invention determines the structure of the CPRI frames andLTE frames by observing the data on the CPRI link. In the first step,the IQM synchronizes itself with the CPRI data steam as shown at 201. Inthe second step, a number of parameters are extracted from the datastream that partially define the structures in question as shown at 202.In the third step, a trial and error discovery process is utilized toextract the remaining parameters as shown at 203.

Refer now to FIG. 9, which is a flow chart of step 201 discussed above.In this step, the data stream on the CPRI communication link ismonitored to find a known point within the data stream. Since there areno header records to provide the location in the byte stream of thebeginning of a CPRI frame, the present invention looks for a knownlocation in the byte stream from which other useful data can bedetermined. In one aspect of the present invention, the byte stream issearched for the CB (Comma Byte) value OxBC as shown at 211. Asdiscussed above, this byte is used to delineate hyper-frames. This byteappears at the start of every hyper-frame. However, since there are 150hyper-frames in each CPRI frame, detecting this byte alone does notdefine a unique location in the stream. However, by examining thecontents of specific bytes following the CB, the CPRI line bit rate canbe determined as shown at 212. In addition, the hyper-frame number ofthe hyper-frame in question can also be determined by examining otherlocations in the hyper-frame as shown at 213. The hyper-frame number ofthe current hyper-frame is encoded in the first byte of the control wordat the beginning of the 64th basic frame of each hyper-frame. Byobserving this hyper-frame number, the number of hyper-frames that mustbe processed until the next full CPRI frame is started can bedetermined, and hence, the IQM can then be synchronized with the REC.

Refer now to FIG. 10, which is a flow chart of step 202. The contents ofbytes following the CB are a function of the CPRI line bit rate and areprovided in the CPRI standard, and hence, will not be discussed indetail here. It is sufficient to note that by examining the contents ofa predetermined set of words relative to the word containing the CB, theCPRI line bit rate can be unambiguously determined as shown at 221. Forexample, if a line rate of 2457.6 is being used, each control word willhave four bytes. The first byte has BC in hex (i.e., the CB value). Thenext three bytes will have values 50, C5, and 50 in hex. The IQ valueswill start after these four bytes. Hence, if this sequence is observed,the line bit rate must be at least 2457.6. If the line bit rate were4915, the control word would have eight bytes, the first four of whichwould be BC, 50, C5, 50 followed by 50 repeated four times.

Given the CPRI line bit rate, the word size and IQ data block size aredetermined as well (see Table 2, above) as shown at 222. Given the wordsize, the CPRI basic frame size in bytes is given by ((word size/8)*16words). The IQ data block size is the frame size minus the length of onecontrol word in bytes.

As noted above, some of the parameters needed to monitor the LTEtransmissions in a particular sub-carrier and slot need to be determinedby trial and error. Hence, data values that can be deduced from the CPRIframe control data and which have corresponding values in the LTE framesub-carrier and slot structure are useful in the trial and error phase.One such data value is the LTE eNodeB frame number. This number isencoded into the control sub-channel of the CPRI frames and is extractedby the present invention as shown at 223. As will be explained in moredetail below, this number is useful in testing assumptions about thestructure of the LTE frames. In particular, the first byte of thecontrol word found in the 128th and 192nd basic frames of the currenthyper-frame encodes the corresponding LTE eNodeB frame number. ThePhysical Broadcast Channel in the LTE also conveys a frame numberrelated to this eNodeB frame sequence number. Typically, the mostsignificant 8 bits of the 11 bit number encoded in the CPRI frames arefound in the Physical Broadcast Channel.

Refer now to FIG. 11, which illustrates the third step of the flow chartshown in FIG. 8. The rest of the system parameters, such as the I and Qsample sizes, number of antenna carriers, LTE system bandwidth, etc. canonly be determined through a trial and error process. That is, aconfiguration is assumed as shown at 231. The configuration is one ofthe possible configurations specifying each of the remaining parameters.The data from the CPRI frames are demodulated assuming the configurationas shown at 232. The contents of one or more known field values in theLTE frame are tested as shown at 233 to determine if the demodulatedvalues are consistent with the LTE model. If the demoduled valuesresulting from the demodulation of the corresponding IQ values are notconsistent with the known parameters or configuration, a new model isassumed and the process is repeated as shown at 234. If the demodulatedvalues agree with the assumed model, it can be assumed that theremaining structures have been determined, and the process exits.

This process can be simplified by exploiting the known LTE structure andhow it is marshaled onto the CPRI links. As noted above, the LTE framenumber is encoded in the CPRI frames and in the resultant LTE frames ata known location. If the demodulated data for the resource elements thatshould contain the LTE frame number do not contain data consistent withthe known value from the CPRI frames, the model being tested isinconsistent. In addition, for each possible LTE bandwidth, there arethree LTE signals of interest that occupy the six RBs around the DCsub-carrier. Thus to determine these other system parameters one needsto collect the IQ samples making up these six RBs over slots 0 and 1 ofthe LTE frame and by trial and error of demodulation, decoding andcorrelation to determine the corresponding parameters.

For example, to discover all the antenna carriers, the process has to berepeated iteratively for each bandwidth over the recovered IQ values.Once the first antenna carrier has been discovered, the I and Q samplesize and whether the I and Q bits are interleaved and the sample size ofany other subsequent antenna carriers are also determined. Since the LTEsignals are synchronous, multiplexing antenna carriers of differentsizes or different bandwidths is not feasible. Hence, in one aspect ofthe invention, it is assumed that once the size of the first antennacarrier has been discovered, any other antenna carriers will be of thesame sample size and will be used to support the same LTE bandwidth overthe current CPRI link.

In some cases, the number of antenna carriers can be inferred by thepresence of padding bytes in the records. For example, padding bytes areoften inserted at the end of the record after the various antennacarrier data. Hence, finding an antenna carrier entry followed by astring of “0s” implies that the last antenna carrier entry has beendiscovered.

The algorithm for determining the LTE parameters involves postulating amodel consisting of one of the possible configurations in terms ofbandwidth, and CP. The parameters associated with that configuration areused to determine the location of the useful samples for a given symbol.An FFT is performed on the useful samples to arrive at a set of symbolvalues for each sub-carrier in the assumed model. Testing those symbolvalues will determine if the values are consistent with the model basedon an LTE system having the assumed parameters. If the symbols are notconsistent with the model, a different model is selected.

In determining if the model is consistent with the observed traffic, thereference/pilot sub-carriers and guard sub-carriers discussed above areuseful. In addition, as noted above, the Physical Broadcast Channelconveys the frame sequence number or a number that can be computedtherefrom, in a known slot. Hence, if this value is not found at theknown location, the model is incorrect, and a new model must be assumed.

It should be noted that the discovery process of the present inventioncan be performed on line or off line on recorded data from the linkbetween the REC and RE. The configuration parameters are expected toremain constant over long periods of time. Hence, the data can besearched using computational platforms that have significantly morecomputing power than those needed to monitor the transmission link oncethe configuration is known. The present invention can be practiced onany suitable computing platform that can acquire the frames on the CPRIlink. Such platforms can include special purpose hardware for recordingthe transmissions between the REC and the RE.

Given a known configuration, a table can be constructed that providesthe starting index in a CPRI frame for any particular symbol/sub-carrierin the LTE system. Hence, the monitoring system can rapidly extract thedesired time IQ samples and recover the symbol in question. Since datatransmissions are allocated in RBs having a plurality of adjacentfrequency bands, the FFT that recovers all of the symbols at a giventime location also supplies all of the symbols for the assigned RBs atthat symbol time location.

The above-described embodiments have utilized an LTE communicationsystem that transmits frames using CPRI frames. However, the method ofthe present invention can be applied to other communication systems thatutilize CPRI frames. In general, the underlying communication system hasits own broadcast frame structure that is incorporated into the CPRIframes. The communication system frames will be referred to as thebroadcast frames in the following discussion. The broadcast frames arethe frames that govern the communications between UE and the RE. Forexample, the broadcast frames for the LTE communication discussed aboveare shown in FIG. 4. The CPRI frames encapsulate the broadcast frames.However, the CPRI frame structure is not totally fixed across allsystems and underlying communication systems. In addition, locating thebeginning of each CPRI frame in the transmissions between the REC and REalso presents challenges. The present invention provides a mechanism fordetermining the start and length of each of the CPRI frames and a numberof parameters that are related to the CPRI encapsulation so that the IQdata that defines the broadcast frames can be extracted.

The manner in which the data that is transmitted and received by the REis packed into the CPRI frames can be different for different underlyingcommunication systems. However, there are a finite number ofpossibilities for the broadcast frames and CPRI frames that encapsulatethese broadcast frames once the CPRI frame characteristics that areindependent of the communication system have been recovered from thecontrol block in the CPRI frame. Typically, CPRI frame characteristicsthat are independent of a model are determined before a model of thecommunication system is selected to reduce the number of possible modelsthat must be considered. The remaining configuration data is determinedby selecting a model for the communication system and using that modelto generate corresponding “candidate” broadcast frames from therecovered IQ baseband data in the CPRI frames. The model assumes anunderlying communication system such as GSM, LTE, UMTS, etc. For eachunderlying communication system there will be a number of possibleimplementations.

The manner in which the broadcast frames are mapped to the CPRI framesalso depends on the underlying communication system. For example, in aGSM system, 13 GSM broadcast frames are mapped on six CPRI frames. Sothe model must also assume one of the possible implementations inaddition to the type of communication system. If the model is correct,the data in the candidate broadcast frames will be consistent with thecommunication system on which the model is based and the implementationof that communication system. If the model is not correct, the candidatebroadcast frames will be inconsistent with the assumed communicationsystem and implementation, and a new model must be chosen.

The manner in which consistency is determined will also depend on theunderlying communication system. However, each communication system mustpresent broadcast frames that are recognized by UE entering a cell. A UEentering a cell of a particular communication system must be able todetect the presence of the cell and synchronize itself to the RE in thecell. In general, each cell in a given communication system broadcastsframes that include a plurality of channels and time slots within thosechannels. Typically, one or more of those time slots in a predeterminedchannel of that communication system includes a synchronization codethat is recognized by all UE capable of connecting to the cell that isbroadcasting the broadcast frames.

In one aspect of the invention, once a model has been postulated, thecorresponding broadcast frames are generated by the present inventionfrom the IQ pairs in the CPRI frames. The corresponding channel and timeslots associated with the synchronization code are then examined todetermine if the expected synchronization code is present. If thesynchronization code is not present, the model is inconsistent with thedata in the CPRI frames, and hence, a new model must be chosen from theset of possible communication systems and implementations.

In LTE communication system model, the primary synchronization signal islocated in the last OFDM symbol of the first time slot of the firstsub-frame. This signal is referred to as the PSS in LTE communicationsystems. The LTE communication also provides a secondary synchronizationsignal (SSS). The SSS symbols are located in the same sub-frame as thePSS at predetermined locations within that sub-frame. Hence, decodingthe sub-frame in question allows the present invention to examine thesynchronization symbols. If the symbols are not consistent with the LTEmodel, a new model must be explored.

In UMTS communication system model, the UMTS broadcast frame size is 10ms long; hence, one UMTS broadcast frame is transmitted in one CPRIframe. Unlike LTE, however, UMTS is not OFDM based. Instead each 10 msradio frame is divided into 15 slots. Each slot is made up of 2560 pairsof IQ samples at a selected bit-width. The individual channels in thetime slots are multiplexed using code division multiplexing rather thanfrequency division multiplexing.

Each time slot in a UMTS communication system has a number of separatechannels that can be decoded. Two of these channels include codes thatcan be used to test the consistency of a particular model. Thesechannels are referred to as the Primary and Secondary SynchronizationChannels in UMTS. The Primary Synchronization Channel is a downloadchannel that transmits an unscrambled known code during the firstportion of each time slot. The same code is used by all the cells of aUMTS communication system so that a UE can easily detect the presence ofa UMTS cell and synchronize itself with the cell. If this code isdetected in the broadcast frame at the proper location in the timeslots, the broadcast frame is consistent with a UMTS communicationsystem.

The consistency of the model can be further tested in a UMTScommunication system by looking at the contents of the SecondarySynchronization Channel. The Secondary Synchronization Code is limitedto a known plurality of codes in a second channel of the broadcastframes. Hence, finding one of these codes further ensures consistencywith the model. The specific secondary code provides the code group usedfor all the other channels. This code group is employed to correlatesymbol-by-symbol and identify the “primary scrambling code” over theprimary common pilot channel. On detecting this last code, one candecode the broadcast frames and the cell specific broadcast controlchannel information. Hence, testing for this second synchronization codealso provides the implementation data needed for decoding specific timeslots and channels.

A similar mechanism can be employed in GSM communication system model.The GSM broadcast frame structure utilizes time division multiplexingtechniques and frequency division multiplexing techniques. The bandwidthis first divided into 124 parallel frequency channels of 200 KHz each,and these are shared using eight slots of time duration 577microseconds. This timing and slot structure for frequency channels isvery suitable for toll voice quality transmissions, for which GSM wasoriginally intended. In simple terms a GSM broadcast frame is made up ofeight slots with a total duration of 4.615 ms. The CPRI specificationdefines a mapping for GSM which involves 60 ms time period to allowclock synchronisation. Thus 13 GSM frames fit into six CPRI frames,ensuring that the first GSM frame is aligned with the first CPRI 10 msframe.

For the purpose of the present invention, depending on the model'sselected operating frequency, bit-width, and samples per basic frame,the IQ pairs representing the GSM broadcast frames can be extracted. Thebroadcast frames can be demodulated using Gaussian Minimum Shift Keying.After such decoding, each GSM broadcast frame will have been convertedinto its binary bit representation. GSM specification defines a set of“bursts” or packets that fit within a GSM slot. The standard definesfour types of packets to include: access, synchronisation, normal, andfrequency correction packets. These slot structures can be searched toidentify and decode synchronisation bursts. Synchronisation packets aremade up of a total of 148 bits and include tail bits, code bits, guardbits and data bits as defined by the standard. The data bits will carrythe base station, cell, and zone identification as well as networkaccess frequency. When recovered, these values can be correlated withinformation known about the system or transported in the CPRIsynchronisation channel.

In another aspect of the invention, data in the control block of theCPRI frames that is specific to the underlying communication system andwhich constrains data in the broadcast frames is used as a consistencycheck by comparing the decoded data in the broadcast frames to the datapredicted using the data in the control block. The eNodeB frame numberthat must be consistent with control word data in the CPRI frames thatwas discussed above with reference to LTE frames is an example of datathat can be used to test consistency.

The present invention also includes a computer readable medium thatstores instructions that cause a data processing system to execute themethod of the present invention. A computer readable medium is definedto be any medium that constitutes patentable subject matter under 35U.S.C. 101, and excludes any medium that does not constitute patentablesubject mater under 35 U.S.C. 101. Examples of such media includenon-transitory media such as computer memory devices that storeinformation in a format that is readable by a computer or dataprocessing system.

The above-described embodiments of the present invention have beenprovided to illustrate various aspects of the invention. However, it isto be understood that different aspects of the present invention thatare shown in different specific embodiments can be combined to provideother embodiments of the present invention. In addition, variousmodifications to the present invention will become apparent from theforegoing description and accompanying drawings. Accordingly, thepresent invention is to be limited solely by the scope of the followingclaims.

What is claimed is:
 1. A method for operating a data processing systemto determine one or more operational parameters of a communicationsystem comprising an REC and an RE that communicate with one anotherover a data link utilizing a plurality of CPRI frames, said REtransmitting and receiving broadcast frames, said method comprising:copying said CPRI frames from said data link at a location between saidREC and RE, said location being different from said REC and said RE;synchronizing said data processing system with said CPRI frames;determining a plurality of CPRI frame characteristics from said CPRIframes by examining a plurality of predetermined locations in said CPRIframes; and using said plurality of CPRI frame characteristics, one ormore of said CPRI frames, and a first model of said communication systemto provide a first broadcast frame that would be generated by said oneor more CPRI frames if said first model accurately described saidcommunication system; and testing said first broadcast frame todetermine if said first broadcast frame is consistent with said firstmodel, assuming that said first model accurately describes saidoperational parameters of said communication system.
 2. The method ofclaim 1 wherein said CPRI frames comprise a first byte in a data streamon said data link, and wherein synchronizing said data processing systemwith said CPRI frames comprises: searching said CPRI frames for saidfirst byte to determine a hyper-frame boundary; and examiningpredetermined locations relative to said first byte to determine anumber of bytes between said hyper-frame boundary and said first byte ofa subsequent CPRI frame on said data link.
 3. The method of Claim Iwherein said plurality of CPRI frame characteristics comprise CPRI framecharacteristics that are independent of said first model, said CPRIframe characteristics that are independent of said first model beingdetermined before testing said first broadcast frame.
 4. The method ofclaim 3 wherein said CPRI frame characteristics that are independent ofsaid first model comprises a CPRI line bit rate used in transmissions onsaid data link.
 5. The method of Claim I wherein determining saidplurality of CPRI frame characteristics includes determining a number ofantenna carriers used in the communication system.
 6. The method ofclaim 5 wherein determining the number of antenna carriers includessearching for a string of padding bytes within the one of the CPRIframes.
 7. The method of claim 1 wherein providing said first broadcastframe comprises extracting IQ data values that depend on said firstmodel from said one of said CPRI frames, and determining symbolsspecified by said extracted IQ data values that would be transmitted bysaid first broadcast frame if said first model accurately describes saidcommunication system.
 8. A method for operating a data processing systemto determine one or more operational parameters of a communicationsystem comprising an REC and an RE that communicate with one anotherover a data link utilizing a plurality of CPRI frames, said REtransmitting and receiving broadcast frames, said method comprising:copying said CPRI frames from said data link at a location between saidREC and RE, said location being different from said REC and said RE;synchronizing said data processing system with said CPRI frames;determining a plurality of CPRI frame characteristics from said CPRIframes by examining a plurality of predetermined locations in said CPRIframes; and using said plurality of CPRI frame characteristics, one ormore of said CPRI frames, and a first model of said communication systemto provide a first broadcast frame that would be generated by said oneor more CPRI frames if said first model accurately described saidcommunication system; and testing said first broadcast frame todetermine if said first broadcast frame is consistent with said firstmodel, assuming that said first model accurately describes saidoperational parameters of said communication system; wherein providingsaid first broadcast frame comprises extracting IQ data values thatdepend on said first model from said one of said CPRI frames, anddetermining symbols specified by said extracted IQ data values thatwould be transmitted by said first broadcast frame if said first modelaccurately describes said communication system, wherein said determinedsymbols comprise synchronization symbols in said first broadcast framethat allow a UE in a cell transmitting said first broadcast frame tosynchronize said UE with transmissions from said cell, and whereintesting said first broadcast frame comprises comparing saidsynchronization symbols in said first broadcast frame to values thatdepend on said first model.
 9. The method of claim 8 wherein said firstmodel comprises an LTE communication system model and wherein saidsynchronization symbols in said first broadcast frame comprise a primarysynchronization signal in said LTE communication system model.
 10. Themethod of claim 8 wherein said first model comprises a UMTScommunication system model and wherein said synchronization symbols insaid first broadcast frame comprises a code in a primary synchronizationchannel in said UMTS communication system model.
 11. The method of claim8 wherein said first model comprises a GSM communication system modeland wherein said synchronization symbols in said first broadcast framecomprises a synchronization packets in said GSM communication systemmodel.
 12. The method of claim 1 wherein testing said first broadcastframe comprises determining symbols in said first broadcast frame andcomparing said determined symbols with a value encoded in a controlblock in one of said CPRI frames.
 13. The method of claim 12 whereinsaid first model defines an LTE communication system and wherein saiddetermined symbols comprise an eNodeB frame number.
 14. The method ofclaim 1 further comprising: choosing a second model for saidcommunication system, said second model being different from said firstmodel when said testing determines that said first broadcast frame wasnot consistent with said first model; using said plurality of CPRI framecharacteristics, and said second model to provide a second broadcastframe that would be generated by said one or more CPRI frames if saidsecond model accurately described said communication system; and testingsaid second broadcast frame to determine if said second broadcast frameis consistent with said second model.
 15. The method of claim 1 whereintesting said first broadcast frame comprises: defining a relationshipbetween locations in said one or more CPRI frames and symbols in saidfirst broadcast frame; and selectively decoding data in said one or moreCPRI frames corresponding to a specified symbol location in said firstbroadcast frame without decoding data corresponding to a differentsymbol location in said first broadcast frame.
 16. A non-transitorycomputer readable medium comprising instructions that cause a dataprocessing system to execute a method for operating said data processingsystem to determine one or more operational parameters of acommunication system comprising an REC and an RE that communicate withone another over a data link utilizing CPRI frames, said RE transmittingand receiving broadcast frames, said method comprising: receiving a copyof said CPRI frames from said data link at a location between said RECand RE, said location being different from said REC and said RE;synchronizing said data processing system with said CPRI frames;determining a plurality of CPRI frame characteristics from said CPRIframes by examining a plurality of predetermined locations in said CPRIframes; and using said plurality of CPRI frame characteristics, one ormore of said CPRI frames, and a first model of said communication systemto provide a first broadcast frame that would be generated by said oneor more CPRI frames if said first model accurately described saidcommunication system; and testing said first broadcast frame todetermine if said first broadcast frame is consistent with said firstmodel, assuming that said first model accurately describes saidoperational parameters of said communication system.
 17. Thenon-transitory computer readable medium of claim 16 wherein providingsaid first broadcast frame comprises extracting IQ data values thatdepend on said first model from said one of said CPRI frames, anddetermining symbols specified by said extracted IQ data values thatwould be transmitted by said first broadcast frame if said first modelaccurately describes said communication system.
 18. The non-transitorycomputer readable medium of claim 17 wherein said determined symbolscomprise synchronization symbols in said first broadcast frame thatallow a UE in a cell transmitting said first broadcast frame tosynchronize said UE with transmissions from said cell, and whereintesting said first broadcast frame comprises comparing saidsynchronization symbols in said first broadcast frame to values thatdepend on said first model.
 19. The non-transitory computer readablemedium of claim 16 wherein testing said first broadcast frame comprisesdetermining symbols in said first broadcast frame and comparing saiddetermined symbols with a value encoded in a control block in one ofsaid CPRI frames.
 20. The non-transitory computer readable medium ofclaim 16 wherein said plurality of CPRI frame characteristics compriseCPRI frame characteristics that are independent of said first model,said CPRI frame characteristics that are independent of said first modelbeing determined before testing said first broadcast frame.